Seasonal pressures

Venus Pax · Post by **Venus Pax** » Thu Jul 05, 2007 7:02 pm

Lee's manual states that "a load you developed in winter may be too hot next summer" (110).

I'm taking this to mean that the powder charge should be lightened during summer months as opposed to winter months.

Since winters in the southern part of Texas are mild, how much should one's powder charge vary from season to season?
In other words, I'm wondering what types of temperature extremes the author was alluding to when he wrote this.

flintknapper · Post by **flintknapper** » Thu Jul 05, 2007 7:36 pm

VP,

If you are not already approaching maximum loads....then I wouldn't worry about the difference.

Some powders (propellants) are more sensitive to temperature than others. Propellants are either single based (nitrocellulose) or double based (also containing a percentage of nitroglycerin). Obviously, those with a larger amount of nitroglycerin will be affected more than those without (increased temperature= more pressure).

Modern powders have stabilizers among other organic compounds, so burn rate and temperature sensitivity is controlled to some extent.

If you were shooting a compressed load in a .44 magnum....you would have more cause for concern.

You can google "modern gunpowders and temperature change" and probably get more info than you'll want to read.

Kudos to you... for asking an excellent question, especially for someone new to reloading. Smart girl!

Houston1944 · Post by **Houston1944** » Thu Jul 05, 2007 8:32 pm

I have never been concerned about temp / pressure relationship with my pistol target loads. Reloading rifle is a different ball game. I have seen some loads with IMR extruded powders have a large variance due to temperature. A few years ago I was 2 grains below book max in a 270 and was blowing out primers and barely getting the cases to eject while at the range in 100 plus temperatures in August. I was using a chronograph and they were clocking about 200 fps higher than earlier in the year. I still have a few of those and other loads labeled â€œcold weather load onlyâ€?.
Fortunately modern technology has solved this problem. Now I mostly use Hodgdonâ€™s Extreme series powders ( Varget, Benchmark to name a couple) and Alliant Re15. Temperature has very little effect on these powders.

longtooth · Post by **longtooth** » Thu Jul 05, 2007 8:35 pm

If you are using Unique as you did earlier, there will be no worry about temp for sure.

Venus Pax · Post by **Venus Pax** » Thu Jul 05, 2007 9:28 pm

Thanks for the response, guys. I didn't think the temperature would be much of an issue in our climate, but wasn't sure.

I'll keep an eye on things. I'm using Unique, which is nitrocellulose with nitroglycerin. For the bullets I will be using next (precision .45 cal SWC in 200 gr.) the manual gives 5.0 grains of Unique as both a minimum and maximum charge.

I'll test a few out before loading too many.

phddan · Post by **phddan** » Thu Jul 05, 2007 10:07 pm

My speer manual shows 200gr SWC at 4.9 to 5.4 grains of Unique.

Dan

Venus Pax · Post by **Venus Pax** » Fri Jul 06, 2007 9:29 am

phddan wrote:My speer manual shows 200gr SWC at 4.9 to 5.4 grains of Unique.

Dan

Thanks, Dan. That gives me a bit more room.

G.C.Montgomery · Post by **G.C.Montgomery** » Fri Jul 06, 2007 10:25 am

FWIW, temperature is not a huge factor for most reloaders. It can be an issue if your load is right at the high end of the safety margin and you are shooting higher pressure cartridges like .40S&W. It's also a potential concern for or any cartridge that has been pushed beyond it's original design specifications. A prime example would be the old days in IPSC when folks loaded .38Super to make a 180 power factor. The loads I shot in those days weren't published in any manual and were probably well beyond SAAMI would consider "safe" in the first place. You knew you'd gone a little too far if the primers in fired cases looked as if they'd never been hit by a firing-pin.